To this end, a hand-held distance measuring device according to the invention comprises a referencing support, which, more particularly, can be folded out and by means of which angles and changes in alignment of the distance measuring device relative to an external reference object, which is stationary in relation to a reference coordinate system, can be determined. The spatial alignment of the distance measuring device in relation to the reference object can, more particularly, be registered by means of angle measuring devices. Additionally, provision can be made for tilt sensors for determining the alignment in relation to the Earth's gravitational field vector.
Methods and systems for measuring distance are used in many applications. Examples for this include incredibly precise surveying in geodetic applications, and also measurement problems in the field of building installations or for industrial process controls.
For these objects, use is made of stationary, movable or else hand-held distance measuring devices, which perform an optical distance measurement to a selected measurement point. Here, a laser beam is usually emitted and, after reflection at the target, received back and evaluated. Here, the various measurement principles are available for determining the distance, such as e.g. a phase measurement or a time-of-flight measurement.
Particularly in the field of building installation or acceptance of construction work, use is made of portable devices, which are to be held in the hand and which, in respect of a structure to be measured, are applied and then perform a distance measurement to a surface. A distance measuring device suitable for such applications, which is typically hand-held, is described in e.g. EP 0 738 899 and in EP 0 701 702.
Since a measurement point that is visible on the surface to be measured is advantageous for most applications, use is usually made of red lasers as radiation sources for the distance measurement. Using rangefinders from the prior art, this thus allows accuracies down to the millimeter range to be obtained, while having great ease of handling. Using currently available hand-held distance measuring devices, it is possible to perform measurements from one point to another point with a line-of-sight connection. If the target is covered, a tilt sensor can also be used to establish horizontal mass.
One option for determining the distance between two points that can also be applied if there is no line-of-sight connection between the points lies in calculation by means of trigonometry. This is already sufficiently well known from ground-based surveying devices, such as theodolites or total stations.
For establishing a distance a between two spatial points B and C by trigonometry, it is enough to know the distance of these two points from a third point A, as well as the angle α at point A between sides b and c in the direction of points B and C. Then, the length of a can be calculated using the law of cosines:a=√{square root over (b2+c2−2·b·c·cos α)}
Although a conventional hand-held distance measuring device from the prior art allows the distances b and c to the spatial points B and C to be measured exactly, a function for precise and reliable determination of the angle α is generally lacking. For the purposes of the distance calculation, currently available acceleration sensors cannot supply a sufficiently reliable value for α and compasses are susceptible to errors, particularly in internal rooms of buildings; at best, it is possible to establish angles from the vertical with a sufficiently high accuracy and reliability by means of inclination sensors.
The prior art has described various solutions with hand-held distance measuring devices with laser rangefinders, by means of which two points can be sighted simultaneously, wherein an angle can be determined between the emission directions of the two lasers.
The two documents DE 10 2007 043 496 A1 and JP 2008 116 249 A respectively disclose a hand-held distance measuring device which comprises two laser rangefinders which are rotatable in relation to one another, wherein the angle between these is determinable.
By contrast, DE 102 14 742 A1 describes a solution with two hand-held distance measuring devices which are connected to one another in a swivelable manner, wherein the mechanical connection between the two distance measuring devices comprises means for registering the angle.
A disadvantage in all these solutions lies, in particular, in the increased material outlay since two laser measurement modules or even two complete distance measuring devices are respectively required for the measurement.